1. Field of the Invention
The present invention pertains to a method of etching features to different depths, and with different etched surface finishes, in a crystalline substrate. In particular, the invention pertains to a method of etching a system of interconnected, variable depth microfluid reservoirs and channels in a crystalline substrate, such as a silicon substrate.
2. Brief Description of the Background Art
The trend in chemical and biochemical sample analysis, and especially in separation systems such as liquid chromatography and capillary electrophoresis systems, is toward smaller and smaller device dimensions. The smaller dimensions are required in some instances to meet performance requirements, and in other instances provide improved performance or reduced analysis costs. In this regard, miniaturized separation systems provide a variety of benefits as compared with conventional separation systems. Some of these benefits includes: 1) more effective system design; 2) increased speed of analysis; 3) decreased sample and solvent consumption; and 4) the possibility of increased detection efficiency.
Several approaches toward miniaturization of liquid phase analysis systems have been developed in the art. Typically, the analytical instrumentation itself has not been reduced in size; rather, it is the size of a separation compartment, for example, which has been significantly reduced. Miniaturized separation compartments for use in an analytical device often consist of a system of interconnected reservoirs and channels. The reservoirs are used to hold samples of analytes to be separated; the rate at which a sample travels down a channel may be used as a basis for determining the composition of the sample, or as a technique for separating compositions within a sample. The reservoirs are typically formed to hold a liquid volume ranging from about 5 picoliters to about 100 picoliters. The interconnecting channels typically have a cross-sectional area on the order of about 100 μm2 to about 10,000 μm2.
There are problems inherent in the miniaturization of interconnecting channels to such small dimensions. For example, the sidewalls of the channel must be very smooth in order to precisely calculate the exact volume of fluid which can be contained within the channel. Any variation in channel dimensions resulting from non-uniform sidewalls will result in a deviation from the calculated channel volume. Deviation from the calculated channel volume will ultimately affect the results of chemical analyses performed using such separation systems. In addition, sidewall roughness in a channel may affect the fluid-flow characteristics of fluids flowing through the channel, also affecting the analytical results.